Physical Properties of Bacillus Toxins and Their Larvicidal Activity Against Anopheles Arabiensis Mosquito Larvae

Abstract

Purpose: Biological control has been strongly encouraged by using of entomopathoginic bacteria Bacillus thuringiensis and Bacillus sphaericus. The present study monitored the larvicidal effect of Bacillus thuringiesis and Bacillus sphaericus against Anopheles mosquito larvae and the effect of physical factors on the larvicidal potency on mosquito larvae.
 Methodology: Mid-guts of Anopheles mosquito larvae were inoculated on both Blood Agar and MacConkey Agar culture media. Depending on Gram stain to determine gram positive and gram-negative bacteria, and to identify the bacterial cells` morphology. A 1000µl of Bacillus thuringiensis. Sample was heated at 80°C for 12 min and diluted from 10 -1 to l0-8 with sterile normal saline. Bacillus strains were inoculated into Müller Hinton broth media and incubated over-night at 37°C. This time was quite enough to form the spores and crystals. The supernatant fluid was discarded and the cell suspensions were washed with sterile distilled water the process was repeated up to 3 times until spores and crystals were free from debris by using phase contrast microscopy. Collected spores and crystals were kept in sterile containers in fridge until used.
 Results: Fifty-three mid-gut contents of Anopheles arabiensis larvae were identified morphologically and biochemically. Bacillus species were the most prevalent bacteria. The highest larval mortality rate was recorded by 5ml of Bt1 and Bt2 after 24 hrs. of treatment and by 150µl of Bacillus species spore.100% mortality was recorded by the Bacillus spore-crystal mixture. A mortality of 60% was recorded at pH 8.0, by 400 C the mortality rate was 20%at 24 hrs. After 12 hours, the exposure to UV light, larvicidal activity reduced to 40 %. 
 Unique Contribution to Theory Policy and Practices: These findings revealed that both B.thuringiensis and Bacillus sphaericus are a good control agent for Anopheles mosquitoes. More deep investigations are needed to verify the effect of the entomopathogens, which has biological and economic importance in mosquito control. In addition, Intensive studies must be needed to validate reliability.